Method and apparatus for measurement of thickness and warpage of substrates

ABSTRACT

An apparatus comprises one or more pairs of mutually coaxial and opposing linear measuring devices including movable, biased fingers for simultaneously determining the thickness and warpage of a substrate such as a circuit board passing between the fingers. Each measuring device is calibrated to a zero point by bringing the ends of the movable fingers together and recording the distance or position thereof. Data for computation of substrate thickness and warpage measurements is obtained by recording displacement distances or positions of the movable fingers in contact with opposing surfaces of the substrate with respect to the zero point, the thickness and warpage then being calculated. The apparatus may be integrated with an assembly line, including incorporation with an existing piece of equipment, so that substrates exhibiting out-of-specification thickness or excessive warpage may be reworked, discarded or downgraded during the manufacturing process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/642,921, filed Aug. 18, 2003, pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the manufacture ofsemiconductor device assemblies. More specifically, the inventionpertains to a method and apparatus for measuring the thickness andwarpage, or nonplanarity, of substrates for carrying semiconductordevices and the like.

2. State of the Art

In the electronics industry, as well as in many other fields, thesuitability of a particular planar member for use may be dependent uponits planarity, i.e., the degree to which a major surface or surfaces areplanar. For example, many electronic components are formed as assembliesusing semiconductor devices mounted on thin substrates, e.g., circuitboards such as conventional FR-4, FR-5 and BT resin circuit boards.Exemplary semiconductor devices include dynamic random access memory(DRAM) devices, static random access memory (SRAM) devices, flash memorydevices, imagers, and many other devices. An exemplary semiconductordevice assembly may comprise a memory module comprising a plurality ofDRAM semiconductor devices mounted to a substrate in the form of acircuit board.

The thickness of many circuit boards used for such assemblies isgenerally from about 0.02 inch to about 0.125 inch. The steps in circuitboard fabrication generally leave inherent stresses in one or moredirections within a circuit board panel from which individual circuitboards are cut. Cutting of a large board panel into smaller discretecircuit boards relieves some of the inherent stress, resulting in somedegree of warpage of each circuit board. The attachment of semiconductordevices to a circuit board may also introduce stresses, such as whenflip-chip configured semiconductor dice are mechanically andelectrically connected to terminals on the circuit board using solderreflow. Although a limited amount of warping may be generallyacceptable, as may warpage in particular directions, excessive warpageor warpage in other directions (individually and collectively“unacceptable warpage”) causes several problems. Unacceptable warpagemay make installation of a completed assembly into test fixtures orhigher-level packaging, such as a motherboard, difficult because ofboard curvature and nonalignment of electrical connectors. Also,unacceptable warpage affects the assembly packaging process in terms ofdifficulty in satisfactorily positioning the assembly into anencapsulant mold assembly, and nonuniformity of distribution ofencapsulant material on the assembly surfaces and about the base of thesemiconductor devices and their connections to circuit board terminals.As a result, completed but defective semiconductor device assemblies mayneed to be reworked (where possible), discarded or downgraded intoproducts of lower value, reducing overall productivity.

Warpage may occur in any direction. For example, significant warpage mayoccur simply along an X-axis and/or Y-axis of a substrate. Additionally,warpage may occur in directions noncongruent with the conventional X, Y,and Z axes. Warpage in multiple planes or in directions oblique toplanes may be termed “complex” warpage.

Current inspection methods for determining whether a substrate isexcessively warped (or otherwise misshaped) generally utilize visualsystems. Such systems are characterized by the use of either humanvision or machine vision, the latter generally providing a faster andmore reliable quantitative measurement of warpage. An example of such amachine vision-based apparatus is shown in U.S. Pat. No. 6,522,777 ofPaulsen et al. Such systems are complex, fairly slow, very expensive,and have a degree of accuracy which is generally beyond that required indetermining warpage. Use of such machines in determining thickness andwarpage of semiconductor device assemblies such as memory modules addssignificantly to the cost of production.

There exist various types of equipment for measuring thickness. Thecommon manual caliper may be useful for product development but is tootime-consuming for production operations. The web measuring gaugescommon in the paper industry are useful for determining thickness ofsheet materials moving at high speed. Such machines are shown in U.S.Pat. Nos. 4,791,367; 5,132,619 of Typpo, and U.S. Pat. No. 6,145,211 ofTyppo et al. None of these machines is designed for, or capable of,measuring warpage in a substantially rigid substrate.

It would thus be desirable to provide an apparatus and method fordetermining unidirectional or multidirectional warpage in a substratesuch as a circuit board.

It would also be desirable to provide an apparatus and method forsimultaneous measurement of the warpage and thickness of a substrate.

It would be further desirable to provide an automated apparatus andmethod for determining the warpage of each of a stream of substratespassing through an assembly line or other continuous manufacturingenvironment and which, if desired, may be incorporated into existingequipment.

In addition, it would be desirable to provide an apparatus and methodfor determining linear and/or complex warpage of a stream of substratesin a single measurement pass for each substrate.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises, in exemplary embodiments, an apparatusand method for determining at least one dimensional value of asubstantially planar substrate. More specifically, the present inventionenables determination of a degree of warpage in a substrate with opposedsurfaces which are normally (or desirably) planar, or flat. Theapparatus and method are useful for determining both substrate thicknessat various locations on a substrate and nonplanarity (warpage) of anysubstrate with desirably flat surfaces.

In the present invention, at least one caliper gauge including twolinear measurement devices having opposed, movable fingers is mounted incoaxial fashion, finger to finger. A contact member on each finger isconfigured and positioned to contact one of the two opposing surfaces ofan intervening substrate disposed transverse to the fingers. One or moreposition readings for each finger is recorded while in contact with, anddisplaced by, the substrate. A zero reading for calibration of eachfinger is subtracted from the respective measured value. The tworesulting displacement differences are added to determine the substratethickness. By obtaining a plurality of measurements along the X, Y, or Zaxis, linearity may be determined along the axis. Nonlinearity, i.e.warpage, may be characterized along the three axes or in directionsoblique to any axis.

The apparatus for measuring substrate thickness and warpage may employconventional commercial linear measuring devices such as those withfingers having terminal contact members which slide or roll on thesubstrate surfaces. A substrate carrier for disposing and moving asubstrate between the linear measurement devices may comprise a roboticgripper of an assembly line for semicontinuous or continuous measurementand determination of warpage in combination with substrate thickness.

The apparatus is simple yet robust, uses conventional linear measuringdevices, is easily calibrated to zero in a manner such that the accuracythereof remains unaffected by wear of the contact members, and is easilyincorporated into an automated assembly line or other continuousmanufacturing environment.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The nature of the present invention as well as other embodiments thereofmay be more clearly understood by reference to the following detaileddescription of the invention, to the appended claims, and to the severaldrawings herein, wherein:

FIG. 1 is a perspective view of an exemplary prior art substrate showingone-dimensional warpage in a first direction;

FIG. 2 is a perspective view of an exemplary prior art substrate showingone-dimensional warpage in a second direction;

FIG. 3 is a perspective view of an exemplary prior art substrate showingone-dimensional warpage in a third direction;

FIG. 4 is a perspective view of an exemplary prior art substrate showingone-dimensional warpage;

FIG. 5 is a generalized schematic view of an apparatus for measurementof substrate thickness and warpage of the invention;

FIG. 6 is a top view of a set of biased caliper fingers including afirst embodiment of terminal contact members of the invention;

FIG. 7 is a top view of a set of biased caliper fingers including asecond embodiment of terminal contact members of the invention;

FIG. 8 is a top view of a set of biased caliper fingers including athird embodiment of terminal contact members of the invention;

FIG. 9 is a top view of a set of biased caliper fingers including afourth embodiment of terminal contact members of the invention;

FIG. 10 is a perspective view of a specific implementation of anapparatus of the invention for measurement of substrate thickness andwarpage;

FIG. 11 is a frontal view of the specific implementation of theapparatus of FIG. 10 for measurement of substrate thickness and warpage;

FIG. 12 is a frontal view of another embodiment of an apparatus formeasurement of substrate thickness and warpage of the invention;

FIG. 13 is a perspective view of an exemplary substrate indicating aseries of locations at which measurements may be made using theapparatus and method of the invention for determining warpage andthickness of the substrate;

FIG. 14 is a perspective view of an exemplary substrate indicatinganother series of locations at which measurements are made using theapparatus and method of the invention for determining warpage andthickness of the substrate; and

FIG. 15 is a perspective view of an exemplary substrate indicatingcontinuous pathways over which measurements may be made using theapparatus and method of the invention for determining the warpage andthickness of the substrate.

DETAILED DESCRIPTION OF THE INVENTION

In use and operation, and referring to FIGS. 1, 2, 3 and 4, an exemplarypseudo-planar substrate 10 such as a memory module is depicted. The term“pseudo-planar” is used to denote a substrate which is substantiallyplanar and, to the naked eye, may appear to be planar, but which inactuality may exhibit nonplanarity in the form of warpage. The substrate10 is depicted as having two major surfaces which are generallyrectangular in shape and may be subject to variations in thicknessand/or warpage. The degree of warpage shown in the figures is generallyexaggerated for illustrative purposes. The substrate 10 is shown withfirst and second major surfaces 20A and 20B, respectively, which have anominal length 12, a nominal width 14 and nominal thickness 16therebetween. The lateral edges of substrate 10 are designated as edges18A, 18B and the end edges as 22A, 22B. Substrate 10 is pictured ashaving been cut from a larger panel of substrate material (not shown)having internal stress(es) introduced during panel fabrication. Thesubstrate 10 may have other structures mounted thereon, such assemiconductor devices and/or other components, not shown. As a result ofthe internal stress(es), warping in different directions may occur dueto stress relief upon cutting of discrete substrates from the panel. Asshown in FIG. 1, longitudinal warping along the X-axis results inwarpage displacement 26A in the Z-direction transverse to the majorplane of substrate 10, and is defined as displacement of substrate majorsurface 20A from a straight line 24A connecting the end edges 22A and22B of the substrate 10. Line 24A represents the theoretical location ofmajor surface 20A if the substrate 10 was truly planar. The term“warpage” may represent various dimensional attributes of substrate 10;for the purposes of this application, “warpage” represents the actualdisplacement from a straight line 24A representing a plane through theends of a major surface, i.e., a condition of no warping, and will begenerally indicated at a point of maximum displacement.

As shown in FIG. 2, the warpage may also be in the Y-direction, causingdisplacement 26B in a Z-direction between the surface 20A and a line 24Bextending between the lateral edge 18A and lateral edge 18B across thewidth 14. As illustrated in FIG. 3, the warpage may occur in a secondlongitudinal (X) direction and produce warpage displacement 26C betweenedge 18A and a line 24C extending between end edges 22A and 22B in alateral (Y) direction. In FIGS. 1, 2, and 3, the warpage displacement isshown as being unidirectional. FIG. 4 illustrates the case where warpingof a substrate 10 may occur in several directions X and Y, leading totwo measurable warpage displacements 26A and 26B in the same or indifferent directions. It is noted that in FIG. 3, like the lateralwarpage displacement 26C in the Y direction, lateral warpagedisplacement may also alternatively (or additionally) occur in the Xdirection.

FIG. 4 illustrates the case where warping of a substrate 10 may occur inseveral directions X and Y, leading to two measurable warpagedisplacements 26A and 26B in the same or differing directions. Further,where the cut lines from a larger panel are not coincident with stresslines in the substrate 10, a complex warpage pattern may be producedwhich resembles rotative twisting of the substrate instead of, or inaddition to, bowing in one or more directions. Excessive warpage of asubstrate, whether unidirectional, multidirectional, or of a complexpattern, complicates or prevents an effective encapsulant moldingpackaging step and results in module terminals which may not be inproper alignment with the connectors of the higher level assembly towhich it is to be attached.

In the present invention, an apparatus and method have been developedwhich measures the warpage of a pseudo-planar substrate, enablingdetermination of an unacceptable substrate before furthermanufacturing/packaging/testing operations are conducted and increasingyield and overall productivity while decreasing manufacturing cost byeliminating processing of defective substrates. The apparatus isconfigured to take measurements from which both the substrate thicknessand warpage may be determined of the method of the present invention.The apparatus may be combined with or incorporated in, for example andnot by way of limitation, an apparatus for severing substrates such ascircuit boards from a larger panel so that warpage of each substrate maybe determined before the addition of semiconductor devices thereto.Alternatively, or in addition, an apparatus according to the presentinvention may be placed in the manufacturing sequence immediately aftersemiconductor devices as well as other electronic components have beenplaced on and secured to the substrate.

In one embodiment of the invention, depicted in FIG. 5, the apparatusfor determining the thickness 16 and one or more warpage displacements26A-C (any displacement, simple or complex, being referred to herein bythe numeral 26) of a pseudo-planar substrate 10 comprises a calipergauge 40 having two yoke members 42A, 42B respectively mounted on bases44A, 44B. Each yoke member 42A, 42B includes a linear measuring device50A or 50B which is actuatable by an axially movable caliper finger 60Aor 60B having a contact member 52A, 52B at a free, distal end thereof.Linear measuring devices 50A, 50B may comprise commercially availablelinear displacement measurement devices, including without limitationlinear encoders, linear potentiometers, and linear displacementtransducers. Linear encoders may take distance readings optically andemploy either a glass scale or take distance readings magnetically anduse a magnetic scale. In optical encoders, a glass scale is marked withalternating black and clear marks and the encoder outputs a sine orsquare wave responsive to reading the alternating black and clear marksas the encoder head moves past them. In a magnetic type encoder amagnetic scale with alternating N and S poles is employed, and theencoder outputs a sine or square wave as the encoder head moves pastthem. For the present application, the scales would be mounted to asolid base and the encoder heads would be mounted to the probe tips orcaliper fingers 60A, 60B. The caliper fingers 60A, 60B are coaxial abouta common axis 38, carry contact members 52A, 52B and are biased bysprings or other resilient elements, magnetic force, etc., along axis 38to move against opposing surfaces 20A and 20B, respectively, ofsubstrate 10 disposed transversely therebetween, at which point theirdisplaced linear distance positions are individually sensed by the twolinear measuring devices 50A, 50B and recorded in memory 68 forcomputation by a calculating device in the form of computer 70. Acarrier 32 holds and positions the substrate 10 at an attitudesubstantially normal to the contact members 52A, 52B between the yokemembers 42A, 42B for making the measurements at specified correspondinglocations 56A, 56B on the generally parallel surfaces 20A, 20B. Thecarrier 32 is movable by actuator 64 in a plane 62 normal to axis 38 sothat multiple measurements may be readily performed at specific desiredlocations on a substrate 10 as it passes between contact members 52A,52B in a direction perpendicular to the plane of the drawing sheet. Forexample, one measure of warpage may be obtained by recordingmeasurements at as few as three locations on a substrate 10. Preferably,carrier 32 comprises a robotic gripper of an automated assembly linesuch as is found in the manufacture of semiconductor memory moduleswherein semiconductor devices are placed on circuit boards, for example.In one embodiment, carrier 32 is configured to move substrate 10continuously to produce a continuum or semicontinuum of measurementsover the surfaces 20A, 20B. In another. embodiment, carrier 32 may beconfigured for discontinuous movement of substrate 10, stopping at eachof a plurality of predetermined measurement locations. Preferably, thecarrier 32 is configured for movement of substrate 10 to permitmeasurements to (or very near to) the edges 22A, 22B, and/or edges 18A,18B, so that maximum warpage displacement may be determined.

A calibration zero point 66 (see FIG. 9) against which to comparedisplacement of caliper fingers 60A and 60B is obtained for each fingerby simply allowing the two contact members 52A, 52B to move into mutualcontact under their respective axial biases without an interveningsubstrate 10. This method avoids the requirement of otherwisedetermining the exact distance between the linear measuring devices 50Aand 50B. Any wear of the contact members 52A, 52B or differences inlength of fingers 60A, 60B is accommodated without the need forrecalibration by this calibration method. Moreover, it is not necessaryfor the substrate 10 to be positioned precisely equidistant from thelinear measuring devices, as long as the substrate is moved parallel toplane 62, since combined and not individual displacement of contactmembers 52A, 52B provides the desired data. Furthermore, it is notnecessary for the zero point to be in the centerline of the substrate 10when passed between contact members 52A, 52B, inasmuch as the zero pointis obtained by the addition of the two, combined contact memberdisplacement measurements from zero point measurement, rather than theexact point of meeting. Substrate thickness measurements then takenrepresent actual locations on the substrate 10, in a plane which isparallel to plane 62, not necessarily in plane 62. Thus, the substrate10 need not be positioned with its surfaces 20A, 20B precisely parallel(in the X- or Y-axis) to the plane 62 of carrier movement. The warpageresults are obtained by determining any nonlinearity of the measurementson either (or both) surfaces 20A, 20B. The substrate thickness 16 isdetermined by summing the differences from the calibration zero point 66for the two surfaces. Dimensional measurement data is transmitted fromlinear measuring devices 50A, 50B to computer 70 through electricalleads 80, computer 70 then calculating thickness and warpage, if any,for the substrate 10 measured. This data may be stored in memory 68 inassociation with the substrate identity (provided, for example, byscanning a bar code on the substrate 10 prior to passage between contactmembers 52A, 52B) and printed out, displayed on a monitor or otherwisemade available on output device 74. The computer 70 may be configuredwith suitable hardware and software to control movement of carrier 32through actuator 64, in addition to processing data generated fromlinear movement 78 of fingers 60A, 60B relative to respective linearmeasuring devices 50A, 50B, and calculating resulting warpagedisplacement 26A, 26B and/or 26C (in one or more directions) andsubstrate thickness 16. Furthermore, computer 70 may be configured tocause carrier 32 to direct substrates 10 exhibiting nonuniform orout-of-specification thickness, alone or in combination without-of-specification warpage, to a rework or discard location since anyunacceptable variation from acceptable tolerances programmed intocomputer 70 or retrievable from memory 68 are calculated substantiallyin real time.

The linear measuring devices 50A, 50B which may be used in the inventionare commercially available in a wide variety of capacities andprecision. Such devices 50A, 50B may comprise devices often designatedas linear encoders. In this invention, each of the coaxial fingers 60A,60B is biased toward the substrate 10 by, e.g., a spring having a forcewhich is sufficiently large to achieve repetitively accurate results,yet small enough to avoid undue damage or wear on the contact members52A, 52B or any flexure of or damage to substrate 10. Associated witheach linear measuring device 50A, 50B may be a finger retractor (notshown) to retract the fingers 60A, 60B with attached contact members52A, 52B from contact with the substrate 10.

The contact members 52A, 52B may take various forms. Each of the contactmembers 52A, 52B may simply be an end of a finger 60A, 60B. Four of manypossible contemplated configurations enabling biased continuous-contactsliding or rolling movement across a substrate surface 20A, 20B areshown in FIGS. 6, 7, 8, and 9. In FIG. 6, the contact members 52A, 52Bcomprise ball-shaped nodes at the terminus of each finger 60A, 60B. InFIG. 7, the contact members are shown as having ellipticalcross-sections. In FIG. 8, the contact members 52A, 52B are depicted asincluding rollers 76A, 76B which roll across the surfaces 20A, 20B. FIG.9 shows the contact members as roller balls 58A, 58B which are mountedin contact members 52 to generally roll freely in all directions over asubstrate surface.

Turning now to FIGS. 10 and 11, a currently preferred embodiment of ameasurement yoke assembly 48 of a thickness/warpage measurementapparatus 30 of the invention is depicted. Yoke assembly 48 has firstyoke member 42A and second yoke member 42B. Both yoke members 42A, 42Bare mounted on bases comprising base members 44A, 44B, respectively. Thebase members 44A, 44B are shown as being rigidly joined by crossbar 82.Each yoke member 42A, 42B has a clamp end 84A, 84B, respectively, intowhich is clamped a linear measuring device 50A, 50B, respectively. Abiased finger, i.e., shaft 60A, 60B, projects from each of the linearmeasuring devices 50A, 50B, respectively, and these fingers 60A, 60B arecoaxial about axis 38. Linear measuring devices 50A, 50B may takevarious forms, e.g., linear encoders, and are readily availablecommercially. For example, one suitable measuring device is a Sony GaugeProbe, Model DG10BN. A contact member 52A, 52B is mounted on the exposedend of each finger 60A, 60B for contact with the substrate surfaces 20A,20B, which typically are generally mirror images of each other. As shownin FIGS. 10 and 11, substrate 10 includes an exemplary semiconductordevice (unnumbered) mounted thereon. In the illustrated embodiment, thecontact members 52A, 52B comprise rollers 76A, 76B formed of carbide orother hard material, but as already described, other types of contactmembers may be used. As shown, each linear measuring device 50A, 50B haselectrical leads 80 extending therefrom for communication with computer70, memory 68 and output device 74 (FIG. 5). In FIG. 10, the rollers76A, 76B are shown as contacting each other, i.e. at a calibration zeropoint 66 (see FIG. 9). The finger extension distance or position foreach finger 60A, 60B at calibration zero point 66 is recorded for eachcontact member 52A, 52B, respectively. A substrate 10, shown as anexemplary semiconductor memory module, is shown positioned (by acarrier, not shown) ready for measurement in FIG. 10. When measurementof substrate 10 is to be undertaken, substrate 10 is passed in plane 62between the two coaxial contact members 52A, 52B, as shown in FIG. 11.Plane 62 is generally perpendicular to axis 38 of the fingers 60A, 60B.When a desired measurement location on opposed substrate surfaces 20A,20B is reached during travel of substrate 10 between the two contactmembers 52A, 52B, the respective linear positions of fingers 60A, 60Bare recorded.

The measured substrate thickness 16 is then calculated by the followingequation:Thickness 16=(Da minus D′)plus(Db minus D″)

Where D′ is the linear position of finger 60A at zero point 66 and Da isthe linear position of finger 60A at a selected measurement location incontact with a substrate 10, D″ is the linear position of finger 60B atzero point 66 and Db is the linear position of finger 60B at themeasurement location in contact with substrate 10. The foregoingpresumes that finger displacement, as recorded, is maximized in adirection away from zero point 66. If this is not the case, then fingerdisplacement in contact with substrate 10 would be subtracted fromfinger displacement at zero point 66. In either instance, it is thedifference between a zero point and a displaced location of a caliperfinger 60 which provides the desired measurement data. When at leastthree measurements are made at points 56 in a path 28 across thesubstrate surface 20A, as shown in FIG. 13, the warpage displacement 26in that direction may be determined by comparing the distances atcentral measurement point 56B with measurement points 56A and 56C. Adisplacement 26 from linearity in the measured distances indicates thedegree of warpage. As an example, the measured distances (in inches)from respective calibration zero point 66 are determined for the twofingers 60A, 60B, and deviation from a straight line is determined.Location Reading − Zero pt 66 = Displacement Distance 56A (edge) 2.13442.0714 0.0633 (surface 20A) 2.3200 2.2573 0.0627 (surface 20B) Thickness16 at location 56A = 0.0633 + 0.0627 = 0.1250 56B (center) 2.1381 2.07140.0667 (surface 20A) 2.3156 2.2573 0.0583 (surface 20B) Thickness 16 atlocation 56B = 0.0667 + 0.0583 = 0.1250 56C (edge) 2.1338 2.0714 0.0632(surface 20A) 2.3190 2.2573 0.0617 (surface 20B) Thickness 16 atlocation 56C is 0.0632 + 0.0617 = 0.1249

Continuing in the example, a straight line through the measureddistances at locations 56A and 56C along path 28 on surface 20A yields atheoretical distance value of 2.1341. The measured value at location56B, however, is 2.1381. The difference comprises a warpage displacement26A of 0.0040. The warpage displacement 26A may also be calculated forthe opposed surface 20B and is 0.0039. The measurements of thickness 16at locations 56A, 56B and 56C also indicate a slight variation (0.0001)in thickness 16 of substrate 10.

While it would be possible to measure warpage by contact of a contactmember 52 of a movable caliper finger 60 from just one side of asubstrate 10, this may cause the substrate 10 to deform, particularly ifthe substrate is very thin or otherwise of marginal rigidity. However,by placing substrate 10 between two equally biased contact members 52A,52B, for example, caliper fingers 60A, 60B will track the naturalcurvature, if any, of substrate 10. Further, by using two measurementsfrom opposing sides of a substrate 10, obviously erroneous measurementsmay be easily detected if the linear distances measured from one side ofthe substrate 10 do not closely track each other within a predeterminedthickness variation tolerance for the substrate 10. In other words, thecurvature of warpage measured from each side of a substrate 10 shouldcoincide but for variations in substrate thickness.

As shown in FIG. 13, warpage displacement 26 may also be determined atpoints 56 in a path 29 perpendicular to path 28, or warpage displacement26 may be determined in both directions 28 and 29 in the same procedureby moving the substrate 10 in two axes. Carrier 32 may be configured,for example, to move a substrate 10 perpendicularly in plane 62 beforeor after moving substrate 10 horizontally between fingers 60A, 60B.

A variation of the apparatus 30 of FIGS. 10 and 11 is depicted in FIG.12. In this variation, a plurality of caliper gauges 40, each withopposing contact members 52A, 52B, is mounted to a yoke assembly 48 tosimultaneously determine thickness 16 at locations 56 along a pluralityof paths, generally three. In this example, measurements are made ateach of points 56A, 56B, 56C, 56D, 56E, 56F, 56G, 56H, and 56J alongthree paths 28A, 28B, 28C ac surface 20A of a substrate 10 (see FIG.14). The opposite surface 20B will generally be characterized as amirror image of surface 20A. As a result, warpage displacement andsubstrate thickness 16 may be determined in three longitudinal paths28A, 28B and 28C, and the same determinations made along threecross-directions 29A, 29B, and 29C. Thus, the determinations arecompleted in a single pass, and warpage, including any complex warpage,may be readily characterized in two directions. It should be noted thatlinear measuring devices 50A, 50B, 50C, 50D, 50E, 50F may be adjustedupwardly and downwardly with respect to the path of a substrate 10 toaccommodate wider or narrower substrates and for placement to avoidcomponents such as semiconductor devices mounted on a given substrate10.

As depicted in FIG. 12, three pairs of coaxial, movable caliper fingers,i.e., 60A and 60B, 60C and 60D, and 60E and 60F have respective contactmembers 52A and 52B, 52C and 52D, and 52E and 52F for contacting thesubstrate 10. The contact members are shown as including rollers 76A,76B as depicted in more detail in FIG. 8. Each finger 60A through 60Factuates its own linear measuring device, for example, fingers 60A and60B actuate linear measuring devices 50A and 50B, respectively.Measurements are transmitted through leads 80 to a computer 70, memory68 and output device 74 (see FIG. 5). Thus, complex warpage such assubstrate twisting may be determined easily from the plurality of datapoints which may be provided both longitudinally along and laterallyacross a substrate 10. All of the contact members 52A, 52B . . . 52F arecalibrated simultaneously to a zero point 66 when a substrate 10 is notin the caliper gauge.

In each of the above embodiments of the invention, it may be noted thatwhile following a distance measurement, the caliper fingers 60A, 60B . .. 60N may be retracted and the substrate 10 moved to the nextmeasurement location. Alternatively, and more preferred for speed andthe capability for continuous measurement, the contact members 52A, 52B. . . 52N of fingers 60A, 60B . . . 60N are not retracted betweenmeasurements, but are displaced against their respective biases bypassage of substrate 10 and simply slide or roll on the substratesurfaces 20A, 20B as substrate 10 passes therebetween. A program incomputer 70 may be used to control the operations of the substratecarrier 32 and linear measuring device(s) 50. The program may includeretraction of the caliper finger(s), for example, where there areinterfering components such as semiconductor devices mounted on thesubstrate 10, where a portion(s) of the substrate is cut out, or when asubstrate 10 approaches for measurement by the apparatus.

In another embodiment as depicted in FIG. 15, measurements may be takenin a once-through continuous manner over the surfaces 20A, 20B, enablinga complete warpage/thickness analysis along every point in threeparallel paths 28D, 28E, and 28F. Cross-direction warpage may becomputed continuously along any portion of the paths, or may berestricted to particular desirable cross-path(s) 29X comprisingmeasurement points 56K, 56L and 56M on the surfaces 20A, 20B, including,if desired, cross-paths 29D, 29E and 29F. If desired, a virtualrepresentation of the substrate planarity, or lack thereof, may begenerated and displayed against a baseline representing an idealsubstrate, or at least one within specified planarity tolerances.

As already shown, the apparatus and method of the invention offers manyadvantages. First, accurate measurements of substrate thickness andwarpage in more than one direction may be performed. The apparatus maybe placed as part of an assembly line using automated substrate handlingequipment. Zero calibration of the linear measuring devices 50 issimple, i.e., merely bringing the corresponding contact members 52together and recording the distance or position measurements of fingers60 within the two linear measuring devices 50. These measurementscomprise the calibration zero points 66 for each linear measurementdevice. The apparatus of the invention may be formed from commerciallyavailable linear measuring devices 50, computer 70, memory 68 and outputdevices 74, such as a computer screen, printer, video, etc.

While the present invention has been disclosed herein in terms ofcertain exemplary embodiments, those of ordinary skill in the art willrecognize and appreciate that it is not so limited. Many additions,deletions and modifications to the disclosed embodiments may be effectedwithout departing from the scope of the invention. Moreover, featuresfrom one embodiment may be combined with features from otherembodiments. The scope of the instant invention is only to be limited bythe claims which follow.

1. An apparatus for determining at least one warpage characteristic of asubstantially planar substrate, comprising: a carrier configured forholding and positioning a substantially planar substrate in a plane, thesubstantially planar substrate having first and second substantiallyplanar opposed surfaces parallel to the plane; a first linear measuringdevice including a first movable caliper disposed on one side of theplane and configured for measuring a plurality of first lineardistances, each first linear distance being the distance from a zeropoint location to a location on the first surface of the substrate; asecond linear measuring device including a second movable caliperdisposed on an opposing side of the plane and configured for measuring aplurality of second linear distances, each second linear distance beingthe distance from a zero point location to a location on the secondsurface of the substrate; and a calculation device for calculating theplurality of first and second linear distances and the at least onewarpage characteristic from the plurality of first and second lineardistances.
 2. The apparatus of claim 1, wherein the first and secondmovable calipers each include terminal contact members at the endsthereof for contacting the respective first and second surfaces of thesubstantially planar substrate.
 3. The apparatus of claim 2, wherein thefirst and second linear measuring devices are configured to provide azero point value corresponding to the common zero point location in theform of a linear distance for each of the first and second movablecalipers for use by the calculation device in calculating the first andsecond linear distances.
 4. The apparatus of claim 2, wherein theterminal contact members comprise one of smooth-surfaced enlargements,unidirectional rollers and multidirectional roller balls.
 5. Theapparatus of claim 1, wherein the first movable caliper and the secondmovable calipers are each biased toward the plane.
 6. The apparatus ofclaim 1, wherein the carrier is configured to move the substantiallyplanar substrate within the plane between the first and second movablecalipers.
 7. The apparatus of claim 6, wherein the-carrier is configuredto move the substantially planar substrate in at least one lineardirection parallel to the plane.
 8. The apparatus of claim 7, whereinthe carrier is configured to move the substantially planar substrate ina plurality of directions within the plane.
 9. The apparatus of claim 7,wherein the apparatus is configured to measure the first linear distanceand the second linear distance from the common zero point location in atleast three different locations on the first and second surfaces of thesubstantially planar substrate in association with movement of thesubstantially planar substrate by the carrier in the at least onedirection.
 10. The apparatus of claim 9, wherein the calculation deviceis configured to determine the at least one warpage characteristic ofthe substantially planar substrate from at least some of themeasurements at the at least three different locations.
 11. Theapparatus of claim 8, wherein the apparatus is configured to measure thefirst linear distance and the second linear distance from the commonzero point location in at least three different locations on the firstand second surfaces of the substantially planar substrate in associationwith movement of the substantially planar substrate by the carrier inthe plurality of directions.
 12. The apparatus of claim 11, wherein thecalculation device is configured to determine the at least one warpagecharacteristic of the substantially planar substrate from some of the atleast three first and second linear distance measurements.
 13. Theapparatus of claim 7, wherein the carrier is configured to move thesubstantially planar substrate continuously between the first and secondmovable caliper fingers while in contact therewith.
 14. The apparatus ofclaim 13, wherein the calculation device is configured to determine atleast one warpage characteristic of the substantially planar substratefrom at least some of a plurality of first and second linear distancemeasurements taken along a line of contact with the substantially planarsubstrate by the first and second movable caliper fingers.
 15. Theapparatus of claim 1, wherein the carrier comprises a robotic gripper.16. The apparatus of claim 1, wherein the first and second linearmeasuring devices comprise linear encoders, linear potentiometers orlinear displacement transducers.
 17. A method for determining at leastone warpage characteristic of a substantially planar substrate,comprising: placing the substantially planar substrate parallel to aplane; measuring a first linear distance from a common zero pointlocation located within the substantially planar substrate to a firstside of the substantially planar substrate in a location along thesubstantially planar substrate; measuring a second linear distance fromthe common zero point location to a second, opposing, side of thesubstantially planar substrate in the location along the substantiallyplanar substrate; measuring another first linear distance and anothersecond linear distance in another location along the substantiallyplanar substrate; and determining any warpage of the substantiallyplanar substrate by comparing differences in at least the measured firstand second linear distances in the location and the another location.18. The method of claim 17, further comprising determining a thicknessof the substantially planar substrate by adding the measured first andsecond linear distances.
 19. The method of claim 17, wherein the anotherlocation comprises a plurality of predetermined locations.
 20. Themethod of claim 19, further comprising selecting at least some of thepredetermined locations of the plurality to be spaced along alongitudinal extent of the substantially planar substrate.
 21. Themethod of claim 20, wherein the at least some predetermined locationsspaced along a longitudinal extent of the substantially planar substrateare selected to be adjacent a longitudinal edge of the substantiallyplanar substrate.
 22. The method of claim 20, further comprisingselecting at least one other location of the plurality of predeterminedlocations on the substantially planar substrate to be spaced laterallyfrom the at least some of the predetermined locations.
 23. The method ofclaim 19, wherein the plurality of predetermined locations comprises asubstantially continuous path extending longitudinally across at least aportion of the substantially planar substrate.
 24. The method of claim17, further comprising measuring the first and second linear distancesby measuring displacements of first and second opposing elements incontact with the opposing sides of the substantially planar substrate.25. The method of claim 24, further comprising establishing the zeropoint location as a location of mutual contact of the first and secondopposing elements without interposition of the substantially planarsubstrate therebetween.
 26. The method of claim 25, further comprisingbiasing the first and second opposing elements toward mutual contact.27. The method of claim 26, further comprising passing the substantiallyplanar substrate between the first and second opposing elements whilemeasuring the displacements thereof on a plurality of predeterminedlocations on the substantially planar substrate.